A photo of the UCL ReRAM device. Credit: UCL/Adnan Mehonic

The
first purely silicon oxide-based ‘Resistive RAM’ memory chip that can
operate in ambient conditions—opening up the possibility of new
super-fast memory—has been developed by researchers at UCL.

Resistive
RAM (or ‘ReRAM’) memory chips are based on materials, most often oxides
of metals, whose electrical resistance changes when a voltage is
applied—and they “remember” this change even when the power is turned
off.

ReRAM
chips promise significantly greater memory storage than current
technology, such as the Flash memory used on USB sticks, and require
much less energy and space.

The
UCL team have developed a novel structure composed of silicon oxide,
described in a recent paper in the Journal of Applied Physics, which
performs the switch in resistance much more efficiently than has been
previously achieved. In their material, the arrangement of the silicon
atoms changes to form filaments of silicon within the solid silicon
oxide, which are less resistive. The presence or absence of these
filaments represents a ‘switch’ from one state to another.

Unlike
other silicon oxide chips currently in development, the UCL chip does
not require a vacuum to work, and is therefore potentially cheaper and
more durable. The design also raises the possibility of transparent
memory chips for use in touch screens and mobile devices.

The
team have been backed by UCLB, UCL’s technology transfer company, and
have recently filed a patent on their device. Discussions are ongoing
with a number of leading semiconductor companies.

Dr
Tony Kenyon, UCL Electronic and Electrical Engineering, said: “Our
ReRAM memory chips need just a thousandth of the energy and are around a
hundred times faster than standard Flash memory chips. The fact that
the device can operate in ambient conditions and has a continuously
variable resistance opens up a huge range of potential applications.”

“We are also working on making a quartz device with a view to developing transparent electronics.”

For
added flexibility, the UCL devices can also be designed to have a
continuously variable resistance that depends on the last voltage that
was applied. This is an important property that allows the device to
mimic how neurons in the brain function. Devices that operate in this
way are sometimes known as ‘memristors’.

This
technology is currently of enormous interest, with the first practical
memristor, based on titanium dioxide, demonstrated in just 2008. The
development of a silicon oxide memristor is a huge step forward because
of the potential for its incorporation into silicon chips.

The
team’s new ReRAM technology was discovered by accident whilst engineers
at UCL were working on using the silicon oxide material to produce
silicon-based LEDs. During the course of the project, researchers
noticed that their devices appeared to be unstable.

UCL
PhD student, Adnan Mehonic, was asked to look specifically at the
material’s electrical properties. He discovered that the material wasn’t
unstable at all, but flipped between various conducting and
non-conducting states very predictably.

Adnan
Mehonic, also from the UCL Department of Electronic and Electrical
Engineering, said: “My work revealed that a material we had been looking
at for some time could in fact be made into a memristor.

“The
potential for this material is huge. During proof of concept
development we have shown we can programme the chips using the cycle
between two or more states of conductivity. We’re very excited that our
devices may be an important step towards new silicon memory chips.”

The
technology has promising applications beyond memory storage. The team
are also exploring using the resistance properties of their material not
just for use in memory but also as a computer processor.

The work was funded by the Engineering and Physical Sciences Research Council.

Source: University College London